Disclaimer: I am no expert, and out of these three IEM's, have only heard the M4, and only recently at that.
That out of the way, my primary listening is classic rock, classical/instrumental (think pirates of the caribbean soundtrack), and piano-heavy rock, like Ben Folds. The M4 seems to be very well suited to rock. Most describe the sound as being in between a flat analytical sound and a V shaped signature with boosted treble and bass. They are a very good buy at the current $28 sale price on amazon. Guitars come through very nicely, and the bass is sufficiently punchy, though by my personal preference, I EQ more a V shape to it. There are at least a couple pretty extensive reviews on it, so to not parrot back everything those have said, I will just say that I highly recommend them for some incredible bang for the buck.